xCuts lets you narrow down what shortcut you're looking for in a number of ways, but one of the coolest features of xCuts for me and the rest of the Windows-to-Mac switching bunch is a section specifically covering Windows shortcuts and their Mac equivalents. Aside from that, xCuts covers other system-wide and application-specific shortcuts (including a handy Quicksilver cheatsheet). I'm not huge on Dashboard widgets, but this is one I actually plan on using. xCuts is freeware, Mac OS X only. — Adam Pash